The present invention relates to a conveying device for forming and conveying groups of products.
In the product packaging industry, screw conveyors are used of the type described, for example, in Patent Applications EP-A-0814037, EP-A-0860384, EP-A-98114561.8 and EP-A-98114556, each of which describes a screw having a number of threads or channels, each for receiving a respective product, which is fed, by rotating the screw, along a path defined by guides extending along the screw.
As described in the above patent applications, by appropriately shaping the screw and the associated guides, it is possible to turn the products over by at least 90xc2x0 about at least one of their axes as they are fed along said path.
In particular, EP-A-0860384 describes a group-forming conveying device, which comprises a screw conveyor having an input end where the inlets of the channels are substantially equally spaced about the screw, and an output end where the outlets of the channels are grouped together along a peripheral portion of the screw, so that the screw conveyor receives, at the input, a substantially orderly succession of products, which, as they are fed along said path, are grouped together to form, at the output of the screw, groups, each defined by a number of adjacent products equal to the number of channels.
When used along a product feed line to feed an orderly succession of groups of products to a user machine, a screw conveyor of the above type involves several drawbacks, owing to the groups being formed at a station located at the output end of the screw, and having to be removed from the station by a transfer device, which, on account of the screw structure, is either inaccurate, in the sense of failing to provide for accurately conveying the groups, or is accurate but relatively bulky and expensive.
In fact, when each group is removed from the output end of the screw in a substantially axial direction with respect to the screw, the group can substantially only be removed, as in the case of EP-A-0860384, using a friction device (defined, for example, by a group of conveyor belts) which, by its very nature, is incapable of conveying the group accurately.
Moreover, a friction device fails to provide for controlling the products at the opposite ends of each group, which is particularly damaging when conveying products whose center of gravity may vary from one moment and one product to the next (e.g. boxes filled with particulate material capable of being variously distributed inside the boxes). In which case, the positions assumed by the respective centers of gravity may be such as to cause the products at the opposite ends of each group to topple over.
Conversely, when each group is removed from the output end of the screw in a direction substantially crosswise to the longitudinal axis of the screw, the group can be removed relatively accurately, but only using a pusher, which, to avoid interfering, immediately after removal, with the next group being formed at the output end of the screw, must have at least two degrees of freedom so as to move along an annular path, one portion of which is normally straight and substantially perpendicular to the screw axis, and another portion of which extends substantially parallel to the screw axis. Such pushers are normally fairly bulky and expensive, and result in severe inertial vibration over and above a given operating speed.
It is an object of the present invention to provide a conveying device for forming and conveying groups of products, designed to eliminate the aforementioned drawbacks.
According to the present invention, there is provided a conveying device for forming and conveying groups of products, the device comprising a first and a second conveying unit; a screw conveyor located between said two conveying units; and a first and a second transfer station connecting the screw conveyor to said first and said second conveying unit respectively; said screw conveyor being mounted for rotation in a given direction about an axis, and comprising a first portion having at least one number of helical channels varying in pitch and for receiving respective products from said first conveying unit and forming the products into groups; characterized in that said second conveying unit comprises a pocket conveyor having a number of pockets, each for receiving a respective said group and feeding the group in a given feed direction.